1. Field of the Invention
This invention relates to systems for analyzing fluids, and more particularly to an system for mechanical, electrical, and fluid interconnection of sensors to a blood analyzer.
2. Description of Related Art
In a variety of instances it is desirable to measure the partial pressure of blood gasses in a whole blood sample, concentrations of electrolytes in the blood sample, and the hematocrit value of the blood sample. For example, measuring pCO.sub.2, pO.sub.2, pH, Na.sup.+, K.sup.+, Ca.sup.2+ and hematocrit value are primary clinical indications in assessing the condition of a medical patient. A number of different devices currently exist for making such measurements. Such devices are preferably very accurate in order to provide the most meaningful diagnostic information. In addition, in an attempt to perform these analyses in close proximity to the patent, the devices which are employed to analyze a blood sample are preferably relatively small. Furthermore, it is important to reduce the size of the cavities and pathways through which the analyte must flow in order to reduce the amount of analyte required. For example, performing blood analysis using a small blood sample is important when a relatively large number of samples must be taken in a relatively short amount of time. More particularly, patients in intensive care require a sampling frequency of 15-20 per day for blood gas and clinical chemistry measurements, leading to a potentially large loss of blood during patient assessment. Furthermore, the amount of blood available may be limited, such as in the case of samples taken from a neonate. In addition, by reducing the size of the analyzer sufficiently to make the unit portable, analysis can be performed at the point of care. Also, reduced size typically means reduced turnaround time. Furthermore, in order to limit the number of tests which must be performed it is desirable to gather as much information as possible upon completion of each test.
In one blood analyzer currently in use, a sensor/calibrant package comprises a sensor assembly mounted within a housing. The sensor/calibrant package also comprises a plurality of fluid pouches mounted within the housing. These pouches hold calibrants and flush fluids necessary for the operation of the blood analyzer. A series of tubes and valves within the housing interconnect the sensors within the sensor assembly to each of the fluid pouches. Since the tubes which transport a sample to the sensor assembly are within the housing, the operator of the blood analyzer can not see the sample as it flows into and out from the sensor assembly. Accordingly, the operator cannot determine visually whether the sample has entered the sensor assembly. This can be a significant problem, since the operator may not visually see that a blockage has occurred in the fluid flow path.
A heater assembly is mounted to the housing in order to raise the temperature of the fluids, the sensor assembly, and the sample to be measured. Raising the temperature allows the analysis of the sample to be carried out at a predetermined temperature. Due to the thermal mass of the components and fluids that must be heated, such blood analyzers may not be used for one or more hours after a new sensor/calibrant package has been installed. Furthermore, the need for such a heater substantially increases the cost of the sensor/calibrant package.
In addition to requiring that the sensor/calibrant package be heated, it is necessary to hydrate the sensors within the sensor assembly. Such hydration of the sensors takes one or more hours. Accordingly, the blood analyzer is not operational for one or more hours after installation of a new sensor assembly. In many cases analysis must be performed at regular and closely spaced intervals. Accordingly, if the heating and temperature stabilization time and the hydration time are relatively long, the number of times such analysis can be performed within a particular amount of time (i.e., turn around time) can be limited to a number less than would otherwise be desirable.
The fluid interface between the fluid pouches and the sensor assembly must be controlled to prevent fluid from pouches from flowing to the sensor assembly prior to installation of the sensor/calibrant package be installed in the blood analyzer. This requirement adds a measure of complexity to the mechanical design of the sensor/calibrant package, thus increasing the cost for fabricating the sensor/calibrant package. Furthermore, the complex interface between the sensor/calibrant package and the blood analyzer makes installation of the sensor/calibrant package more difficult, increases the chance that fluid will leak from the sensor, and can potentially increase the length of the fluid path (thus increasing the chance that a clot will occur and increasing the required volume of the sample). A portion of elastomeric tubing which interfaces the sensor assembly to the fluid pouches and a refuse pouch (into which exhausted samples and other fluids are pumped) is stretched over a concave surface. When the sensor/calibrant package is placed within the blood analyzer, a pump arm strokes the tubes in order to create a peristaltic pump, thus increasing the complexity of the mechanical interface between the sensor/calibrant package and the blood analyzer. Further complicating the mechanical interface is the need to provide a mechanism by which the blood analyzer can control the valves within the sensor/calibrant package. A first valve must be rotated to allow a controller within the blood analyzer to configure the fluid path. A set of additional slide valves must be actuated upon installation of the assembly into the blood analyzer in order to open the flow path from each of the fluid pouches.
The sensor assembly has a plurality of sensors formed on a front side of a polymeric substrate along a flow path between an inlet and outlet port. The fluid flow path is formed as a groove in a polymeric substrate. Electrodes are formed in the substrate. The electrodes communicate with a measurement flow channel formed in the substrate. The electrodes also communicate with a measurement flow channel which is formed by the combination of substrate and a cover plate.
The electrical interface between the sensor assembly and electronics external to the sensor assembly is provided through an plurality of contacts fabricated on the rear surface of the substrate. These contacts slide against a spring loaded mating contact in the blood analyzer. As the contacts of the sensor assembly slide against the mating contacts within the blood analyzer, the contacts of the sensor assembly and analyzer are worn down. Therefore, after inserting and removing the cartridge from the blood analyzer a number of times, the electrical connection between the external circuits within the blood analyzer and the sensors within the sensor assembly will be degraded.
Due to the use of electrical slide contacts, the structure of the interface between the elastomeric tubes and the pump, and the configuration of the valve controls, the sensor/calibrant package must first be inserted into the blood analyzer, and then slide generally at a right angle to the insertion angle. This process makes installation of the sensor/calibrant package awkward and increases the risk that either the electrical, mechanical, or fluid interface between the sensor/calibrant package and the blood analyzer will be faulty.
Furthermore, since the sensor is an integral part of the sensor/calibrant package, when a sensor fails (i.e., can no longer perform in accordance with specified parameters) the entire sensor/calibrant package must be replaced.
Accordingly, in as much as installation and fabrication of sensors within a blood analyzer are both cumbersome and susceptible to leaks, and long delays result after installation, it would be desirable to provide an assembly which allows the operator of a blood analyzer to replace merely the sensor assembly with a fast turn around time, no special training, and with highly reliable electrical, mechanical and fluid interface.
The aforementioned parent application solved many of the above enumerated problems of the prior art. However, a number of further improvements are desirable. For example, in the aforementioned system, the sample is introduced into the system through a port in the analyzer and passes through plumbing therein to the sensor cartridge. This has a number of disadvantages such as a longer fluid passage requiring a larger sample. The greater distance of travel of the sample also introduces a greater chance for contamination from gases and other materials.
Another problem is that the fluid passage in the analyzer becomes contaminated, not just from the blood but from calibrant materials which have salts in them.
Furthermore, it would be desirable to provide such an assembly which further allows the user to see a blood sample as it enters, flows through, and exits the sensor assembly.